1. This may be off-topic. 2. In the applicable domain (word-processing), the terms are unambiguously defined. Align relates to one aspect: left or right. Justify relates to aligning both at the same time. 'Center' is relevant in Justify' but not in *align.
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KrisDec 24 '12 at 10:19

To add to the above, align also allows you to vertically line up all matching characters eg a decimal point in a column of figures. Whole number figures without a decimal component align to the left of the decimal, any numbers with a fractional component have the decimal part aligned to the right for however many places.
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mcalexDec 24 '12 at 11:48

Whilst the modern terminology seems to suggest align is the correct phrase, this seems to be a recent innovation.

Certainly I've always used left justified and right justified and fully justified in the typing/typesetting sense... it is only since I've been doing web-based work (noting that HTML/CSS uses align) that I've found myself using align even though I still think of justifing paragraphs.

By way of clarification, text within a paragraph is justified, whereas the paragraph is aligned with respect to the margins (etc). In the accounting sense, the numbers are vertically aligned by the decimal points, whereas the currency symbol is usually left justified

I think you'll find those two terms align and justify were being used a long time before the web and html came into being!
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spiceyokookoDec 24 '12 at 12:48

I don't disagree @spiceyokooko - but they used to mean different things, whereas now they seem to amount to the same (or rather align seems to have usurped justify)... as per the accounting alignment observation
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AndrewDec 24 '12 at 12:53

Aligning on decimal points and commas has nothing to do with text block alignment and was originally for tab settings only. They should not really be used when referring to text block alignment or justification.
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spiceyokookoDec 24 '12 at 13:02

The question “Is it OK to call this option justify or is only align correct?” implies that an option name is sought. Both of those words are verbs. Nouns often are more suitable for use as names than are verbs. Noun forms of the words are justification:

(typography) The alignment of text to the left margin (left justification), the right margin (right justification), or both margins (full justification)

and alignment:

proper or desirable coordination or relation of components (1) or
when two or more things are positioned in a straight line or parallel to each other (2)

It appears that the Collins and Cambridge dictionaries just referenced don't yet recognize special typographical meanings of alignment. Nevertheless, my recommendation is that you use one of the words alignment, positioning, or placement as the name of the option.